Paddy rice harvested from the fields includes a hull surrounding the rice grain. Rice hulls are separated from the paddy rice, usually after the paddy rice has been subjected to processing operations.
There has been considerable effort to find beneficial and profitable uses for the hulls which may be considered as an inevitable product of all rice processing. Rice hulls are disposed of by returning them to the field, or using them in animal litter and in animal feed, or as a carrier and in plastics, and other assorted ways. One of the other major ways in which rice hulls are used is as fuel. To use the rice hulls as fuel, they are simply burned. The burned rice hulls produce an ash which is also used in many ways including in animal litter and in plastics. The ash is also used as a component of refractory material and as a very effective insulating material and to insulate molten steel.
In steel mills, rice hull ash is applied as an insulating covering over ladles of molten steel and tundishes while the molten steel is being held prior to further processing. The insulation effect afforded by this "blanket" of rice hull ash minimizes heat loss from the molten steel.
Use and treatment of rice hull ash has been an active topic in the patent literature. There have been numerous efforts to improve on the basic technology. For example, U.S. Pat. No. 4,442,130 teaches a method for processing rice which utilizes the hulls. In the method, rice hulls are fed into a burner unit where they are burned in two stages to produce ash and relatively clean hot gases. The hot gases are cycled for use in a heat treating phase of the rice.
Unfortunately, one especially undesirable condition persists. Rice hull ash includes small particles which become airborne. These airborne particles can be very irritating as they are essentially a black dust, and they get into the eyes and nose of anyone in the vicinity of the ash. Additionally, these black particles leave a dusty film.